Protective overcoating



Dec. 18, 1945. MlNSK ETAL I 2,391,181

PROTECTIVE OVERCOATING Filed May 2, 1944 PROTECTIVE O VERC'OA TING E MULS ION SUBB/NG' LAYER- WATERPROOF/N6 LAYER SUPPORT WA TERPROOF/NG' LAYER LOUIS M. MINSK K WALTER J .WE YE'R'IIS' T VENDELL H. M DOWELL INVENTORS BY Q MM A TTORNE YS Patented Dem 18, 194s uurrso s'rA'ra-s PATENT orrics raornc'rivr: OVEROOATING Louis M. Minsk, Walter J. Weyerts, and Wendell 1 H. McDowell, Rochester, N. Y., asslgnors to Eastman Kodak Company, Rochester, N. Y., a

corporation of New Jersey 5 Claims.

This invention relates to photographic material, and particularly to a protective overcoating for photographic emulsions.

Various materials such as gelatin and synthetic resins have been used as overcoating layers for photographic emulsions. These layers may be applied before exposure of the photographic emulsion in which case they must be permeable to, or removable in, the photographic developing solutions so that development of the emulsion can take place.

It is frequently desirable to print a photographic negative onto a sensitive photographic emulsion immediately after the negative has been developed and fixed, without resorting to the usual washing and drying steps. When the wet negativ is broughtin contact with the printing material in this way, the negative would stick to the gelatin of the emulsion of the printing material, and the residual hypo in the negative would contaminate the positive emulsion and produce uneven development eflects. Customary gelatin overcoatings on the printing material would not prevent this action and many synthetic resin overcoatings would be susceptible to the action of the water, or, if not affected by the water, would not be removable in the developing solution.

In Batley British Patent 550,775, an emulsion overcoating is described consisting of a resin having free acidic groups, such as polyvinyl acetate phthalate or rosin-maleic anhydride resin. These materials are used as overcoatings for the emulsion to prevent action of the water or hypo on the positive emulsion during the printing operation. The materials disclosed in this patent, however, are not uniformly removable in the developing solution and have not proven satisfactory in practice.

It is, therefore, an object of the present invention to provide a resin overcoating material for photographic emulsions which will permit printing of the emulsions from wet negatives. A further object is to provide an emulsion overcoating material which will be readily removable in alkaline photographic developing solutions, so that development of the exposed emulsion may take place in the customary manner. Other objects will appear from the following description of our invention.

These objects are accomplished by applying to the emulsion of the printing material a layer of a copolymer of methacrylic acid and an alkyl methacrylate. such as methyl-a-methacrylate. In the case of methacrylic acid and methyl-a-methacrylate, a copolymer is produced having the following probable structure:

Flai 21:1 coon dooc where n is a whole number.

The single figure of the accompanying drawing is a sectional view of a printing material constructed according to our invention.

The overcoating material which we propose to use is made by copolymerizing methacrylic acid and an alkylmethacrylate, such as methyl-@- methacrylate, ethyl-a-methacrylate, or butyl-amethacrylate in a suitable solvent, such as ethyl alcohol, using a catalyst, such as benzoyl peroxide. Mixtures of the alkyl methacrylates may also be employed so that a ternary copolymer is produced.

The copolymer produced in this way may be precipitated and isolated from the reaction mixture, or the reaction dope may be diluted to form a. suitable coating solution and coated on the emulsion without isolation of the copolymer. The following examples will illustrate the formation of typical copolymers to be used accordingto our invention.

Example 1 The following ingredients were placed in a 22- liter round-bottom flask, attached through a glass joint to a large reflux condenser:

Methacrylic acid grams Methyl-u-methacrylate do Ethyl alcohol cc 15,100 Benzoyl peroxide grams 14.88

The reaction mixture was heated on a steam bath and maintained at vigorous reflux for 22 to 30 hours. Th resin was then precipitated by pouring the dope into 20 gallons of cold water which was vigorously stirred. The suspension of resin in water was stirred for an additional 20 to 30 minutes during which time anysoft precipitate hardened. The product was obtained in the form of granules and was then washed with eight 20- gallon portions of hot water, allowing 1 hour soaking with each one. The product was dried at 50 C. We have found that the resin may be centrifuged before drying and then dried at room temperature.

If the resin is used for coating without isolating it from the reaction mixture, the resin dope 01)- tained after heating on the steam 'bath for 22 to 1 30 hours may be used directly for coating after dilution with suitable solvents.

Example 2 The reaction mixture was heated on the steam bath under reflux for 19 hours. The dope was then diluted with about an equal volume of absolute alcohol and the resin precipitated by pouring the dope into distilled water. The fibrous precipitate obtained was washed with distilled water.

res Ethyl alcohol (95%) 69 Methyl Cellosolve 8 Water 13 Water is used in the formula to enable coatings of the composition to set in a manner similar to gelatin, during drying. The concentration of resin in the formula is determined somewhat by the particular resin, coating conditions desired, and the viscosity or molecular weight of the resin.

This solution is coated so that after drying a resin concentration of about 0.6 gram per square foot of emulsion surface is obtained.

.The reaction mixture described above contains substantially equal proportions of methacrylic acid and methyl-a-methacrylate, the latter being slightly in predominance. The proportions of methacrylic acid may vary, however, from about 30% to about 60%, and the proportion of methyl-a-methacrylate from about 70% to about 40%.

A typical photographic material constructed according to our invention is shown in the accompanying drawing. As illustrated therein, 10 is the support of baryta-coated paper having on each side waterproofing layers H of cellulose nitrate applied from the following solution:

Grams Cellulose nitrate 1 Methyl alonhnl 40 Butyl alcohol 10 The cellulose nitrate is preferably a high alcohol soluble, low viscosity material, such as one having a methyl alcohol solubility of l lo-100%, a

viscosity of 2 to 5 seconds by the dropping ball method" and a nitrogen content of 11-12%.

The baryta coating side of the support is then coated with a subbing layer i2 of gelatin coated from the following solution:

The subbing layer I2 is followed by a customary gelatino-silver halide emulsion layer 13 and the protective layer ll of the copolymer of methacrylic acid and methyl-a-methacrylate prepared as described above. In some cases, it is desirable to apply a thin gelatin coating over the emulsion before applying the resin layer. It may also be desirable to include plasticizers in the resin dope.

We have found that the coatings prepared as described above ailord adequate protection for the emulsion against the action ofwater and hypo in the negative during the usual contact printing times. The resin layer does not crack or peel from the emulsion during storage of the sensitive material and is readily removable in the alkaline developing solution upon development of the exposed material.

While we have illustrated our invention as being applied to sensitive emulsions carried on paper supports, it is apparent that the hypo protective over-coatings of our invention can also be applied to sensitive emulsion layers on'supports of cellulose esters, synthetic resins; glass or other materials.

Methacrylic acid methyl-a-methacrylate resin grams Ethyl alrnhnl m' 1470 Methyl Cellosolve cc 163 Fuchsine Y grams 6.2 (ii-ethyl 2 benzoxazole) (l-ethyl 2,5-

dimethyl-3-pyrrole) dimethine cyanine iodide (Brooker et al. U. S. 2,298,731)

grams 7.1

if greater plasticity is desired, mixtures of resins can be used, such as a mixture of the above resin with a butyl methacrylate-methacrylic acid copolymer.

The modifications and examples included herein are illustrative only, and our invention is to be taken as limited only by the scope of the ap-- pended claims.

We claim:

l. A sensitive photographic element comprising a support having thereon a light-sensitive emulsion layer and over said layer a layer of a copolymer of methacrylic acid and an alkyl methacrylate insoluble in water but soluble in alkaline photographic developing solutions.

2. A sensitive photographic element comprising a support having thereon a light-sensitive emulsion layer and over said layer a layer of a copolymer of methacrylic acid and methyl-@- methacrylate insoluble in water but soluble in alkaline photographic developing solutions.

3. A sensitive photographic element comprising a paper support having thereon a light-sensitive emulsion layer and over said layer a layer of a resin formed by copolymerizing substantially equal parts of methacrylic acid and methyl-amethacrylate, said resin being insoluble in water, but soluble in alkaline photographic processing solutions.

4. A sensitive photographic element comprising a support having thereon a light-sensitive emulsion layer and a superficial layer of a copolymer of methacrylic acid and an alkyl methacrylate insoluble in water but soluble in alkaline photographic developing solutions.

5. A sensitive photographic element comprising a support having thereon a light-sensitive emulsion layer and a superficial layer of a copolymer of methacrylic acid and methy -amethacrylate insoluble in water but soluble in alkaline photographic developing solutions.

LOUIS M. MINSK. WALTER J. WEYERTS. WENDELL H. MCDOWELL. 

